Performance Considerations; Warm Up; Autozero - Keithley 3700 Series User Manual

Series 3700 System Switch/Multimeter User's Manual
Use the following procedure when testing power circuits:
1. De-energize the circuit using the regular installed connect-disconnect
device. For example, remove the device's power cord or by turning off the
power switch.
2. Attach the test leads to the circuit under test. Use appropriate safety rated
test leads for this application. If over 42V, use double-insulated test leads or
add an additional insulation barrier for the operator.
3. Set the multimeter to the proper function and range.
4. Energize the circuit using the installed connect-disconnect device and make
measurements without disconnecting the multimeter.
5. De-energize the circuit using the installed connect-disconnect device.
6. Disconnect the test leads from the circuit under test.

Performance considerations

Warm up

After the Series 3700 is turned on, it must be allowed to warm up for at least two
hours to allow the internal temperature to stabilize. If the instrument has been
exposed to extreme temperatures, allow extra warmup time.

Autozero

To help maintain stability and accuracy over time and changes in temperature,
the Series 3700 periodically measures internal voltages corresponding to offsets
(zero) and amplifier gains. These measurements are used in the algorithm to
calculate the reading of the input signal. This process is known as autozeroing.
When autozero is disabled, the offset and gain measurements are not
performed. This increases the measurement speed. However, the zero and gain
reference points will eventually drift resulting in inaccurate readings of the input
signal. It is recommended that autozero only be disabled for short periods of
time. The internal temperature references used for thermocouple measurements
are performed regardless of the autozero state because they do not have a
significant effect on measurement speed.
When autozero is enabled after being off for a long period of time, the internal
reference points will not be updated immediately. This will initially result in
inaccurate measurements, especially if the ambient temperature has changed
by several degrees.
3700S-900-01 Rev. C / July 2008
Section 5: Basic Digital Multimeter (DMM) Operation
5-3